Initial size of unilateral pleural effusion determines impact of thoracocentesis on oxygenation

Anatomy and Applied Physiology of the Pleural Space

The unique anatomy and physiology of the pleural space provides tight regulation of liquid within the space under normal physiologic conditions. When this balance is disrupted and pleural effusions develop, there can be significant impacts on the respiratory system. Drainage of effusions can lead to meaningful improvement in symptoms, primarily owing to improvement in the length-tension relationship of the respiratory muscles. Ultrasound examination to evaluate the movement and function of the diaphragm, as well as pleural manometry, have provided a greater understanding of the impact of pleural effusion and thoracentesis.

The Impact of Thoracentesis On Postprocedure Pulse Oximetry

BACKGROUND

Although thoracentesis can offer considerable symptomatic relief to the patient, its physiologic impact on oxygen saturation has not been well established in the literature. This study aimed to evaluate the impact of thoracentesis on postprocedure pulse oximetry (SpO2) in an inpatient population.

METHODS

A retrospective study of patients undergoing thoracentesis from January 2012 to November 2017 was performed. Inclusion criteria were age above 18 and thoracentesis performed in an inpatient setting. Records were reviewed for patient demographics, procedure reports, and laboratory values. SpO2 and FiO2 values were collected before and 6 and 24 hours postprocedure. Multivariable linear regression models were used to evaluate for changes in SpO2 and SpO2/FiO2. Analyses were adjusted for age, sex, serum hemoglobin, effusion etiology, volume removed, nonexpandable lung physiology and procedural complications and FiO2.

RESULTS

A total of 502 patients were included. The mean (SD) age was 60 (14) years, and 53.4% of the patients were male. The most common cause of pleural effusion was malignant effusion (37%). The median (interquartile range) volume of fluid removed was 1400 (1000 to 2000) mL and nonexpandable lung physiology was noted in 35%. There was no significant within-subject difference in 24 hours postprocedure SpO2 compared with preprocedure SpO2. In multivariable analysis, there was a small increase in 24-hour postprocedure SpO2 [β=0.31, 95% confidence interval (0.22, 0.41), P<0.01] and a similar small increase in 24-hour postprocedure SpO2/FiO2 [β=0.84, 95% confidence interval: (0.68, 1.01), P<0.01).

CONCLUSION

Among inpatients undergoing thoracentesis, there is no clinically significant change in SpO2 or SpO2/FiO2 at 24-hours post-procedure compared to pre-procedural SpO2 or SpO2/FiO2.